#include <stdio.h>

int mian()
{
	int number;
	int sum = 0;
	int count = 0;
	
	scanf("%d",&number);
	while(number != -1)
	{
		sum += number;
		count ++;
		scanf("%d",&number);
	}
	
	printf("平均数为%f\n",1.0*sum / count);
	
	return 0;
}